45-58+(-45)+(+58)-3=45-58-45+58-3=(45-45)+(58-58)-3=-3

(-57)-(-12)+3-(-57)=-57+12+3+57=(-57+57)+12+3=15

-(-24)-(-30)+(-24)-30+8=24+30-24-30+8=(24-24)+(30-30)+8=8

-(-12)+(+19)-(+12)+8-19=12+19-12+8-19=(12-12)+(19-19)+8=8

47-(-53)+(-47)-(+53)=47+53-47-53=(47-47)+(53-53)=0

-(+28)+32-(-28)+(-34)=-28+32+28-34=(-28+28)-(34-32)=-2

15-(+72)+(-15)+(+72)=15-72-15+72=(15-15)+(72-72)=0

20-(+46)+(-25)-(-46)=20-46-25+46=(20-25)+(46-46)=-5

28-(-32)+(-28)-32+5=28+32-28-32+5=(28-28)+(32-32)+5=5

-75+(-49)+(+75)+49-12=-75-49+75+49-12=(-75+75)+(49-49)-12=-12

\(...=45-58-45+58-3=-3\)

\(...=-57+12+3+57=15\)

\(...=24+30-24-30+8=8\)

\(...=12+19-12+8-19=8\)

\(...=47+53-47-53=0\)

\(...=-28+32+28-34=-2\)

\(...=15-72-15+72=0\)

\(...=20-46-25+46=-5\)

\(=...28+32-28-32+5=5\)

\(...=-75-49+75+49-12=-12\)

a,4x7x5x5x9

=(4x5)x(9x5)x7

=20x45x7

=900x7=6300

a.200

b.20

           a) 11 + 28 + 24 + 16 + 112 + 9 

             = ( 11 + 9 ) + ( 28 + 112 ) + ( 24 + 16 ) 

             =      20 + 140 + 40

             =   200

           b) 75 - 13 - 17 - 25

            = ( 75 - 25 ) - 13 - 17

             =   50 - 13 - 17 

             = 20

cụ thể hơn cô oi

A, 2 x 26 x 5 =( 5 x 2) x 26

10 x 26

=260                   

 b,4 x 37 x 25 =( 4 x 25) x 26

= 100 x 26

= 3700           

 c, 25 x 5 x 4 x 27 x 2 =( 25 x 4 ) x ( 2x 5) x 27

= 100 x 10 x 27 

= 1000x 27 

=27000

d,28 x 64 + 28 x 36 = 28 x ( 64 + 36 )

= 28 x 100

=2800

 e, 769 x 85 - 769 x 75  = 769 x ( 85 - 75 )

=769 x 10

=7690

f, 56 x 37 + 56 x 63 = 56 x ( 37 + 63 )

= 56 x 100

=5600

a. = 26 x (2 x 5)

   = 26 x 10 =260

b.=( 25x4) x37

   =100 x37=3700

c.=(25x4) x(5x2) x27

   =100 x10 x27

   = 27000

d.=28 x( 64+36)

   =28 x100

  = 2800

e.=769 x( 85-75)

    =769 x10 =7690

f. =56 x(37 +63)

  =56 x100

= 5600

a)    \(\left(-25\right).5.\left(-4\right).2\)

\(=\left[\left(-25\right).\left(-4\right)\right].\left(2.5\right)\)

\(=100.10=1000\)

b)   \(\left(-456\right)-\left(67-456\right)\)

\(=-456-67+456\)

\(=\left(456-456\right)-67\)

\(=67\)

a) ((-25).(-4)).5.2

=100.10

=1000

b) (-456)-67+456

=(-456)+(-67)+456

=0+-(-67)

=-67

c)78.45+-145.78

=78.(45+145)

=78.190

=Tự làm

a) (-25).5.(-4).2

= 5 . ( -4 ) . ( -25 ) . 2

= -20 . ( - 50 )

= 100

b) (-456) - (67 - 456)

= -456 - 67 + 456

= -456 + 456 - 67

= -67

c) 78.45+145.(-78)

= 78 . 45 + ( - 145 ) . 78

= 78 . ( -145 + 45 )

= 78 . 100

= 7800

d) 38.( 62-75) + 62.(-75 - 38)

= 38 . 62 - 38 . 75 + 62 . ( - 75 ) - 62 . 38

= 38 . 62 - 62 . 38 + 38 . 75 + 62 . ( - 75 )

= 0 + 38 . 75 + ( - 62 ) . 75

= 75 . ( - 62 + 38 )

= 75 . ( - 24 )

= - 1800

a) 125.(-4).(-8).7

= 125 . ( - 8 ) . ( - 4 ) . 7

= 1000 . ( - 28 )

= - 28000

c) 72.( 28 - 49) + 28. ( -49 - 72)

= 72 . 28 - 72 . 49 + 28 . ( - 49 ) - 28 . 72

= 72 . 28 - 28 . 72 + 72 . 49 + 28 . ( - 49 )

= 0 + 72 . 49 + ( - 28 ) . 49

= 49 . ( -28 + 72 )

= 49 . 44

= 2156

58 x 75 + 25 x 58 - 58 x 28

= 58 x ( 75 + 25 + 28 )

= 58 x 128

= 7424

58 x 75 + 25 x 58 - 58 x 28

= 58 x (75 + 25 - 28)

= 58 x 72

= 4176

= 4176  nha bn

27/18 - 9/15 = 405/270 - 162/270 = 243/270

14/28 - 25/75 = 1050/2100 - 700/2100 = 6

:0

m _Fe2O3=28.\(\dfrac{75}{100}\)=21g =>n _Fe2O3=​\(\dfrac{21}{160}\)=0,13125 mol

m _CuO=28-21=7 g =>n _CuO=\(\dfrac{7}{80}\)=0,0875 mol

Fe2O3+3H2->2Fe+3H2O

0,13125-0,39375-0,2625

CuO+H₂-to>Cu+H₂O

0,0875-0,0875-0,0875 mol

=>m Fe=0,2625.56=14,7g

=>m Cu=0,0875.64=5,6g

=>n H2=0,39375+0,0875=0,48125mol